Collision Behavior Research Articles

No infinite spin for planar total collision

The infinite spin problem is an old problem concerning the rotational behavior of total collision orbits in the n-body problem. It has long been known that when a solution tends to total collision then its normalized configuration curve must converge to the set of normalized central configurations. In the planar n-body problem every normalized configuration determines a circle of rotationally equivalent normalized configurations and, in particular, there are circles of normalized central configurations. It’s conceivable that by means of an infinite spin, a total collision solution could converge to such a circle instead of to a particular point on it. Here we prove that this is not possible, at least if the limiting circle of central configurations is isolated from other circles of central configurations. (It is believed that all central configurations are isolated, but this is not known in general.) Our proof relies on combining the center manifold theorem with the Łojasiewicz gradient inequality.

The propagation and collision behavior of $$\varvec{\delta }'$$ waves in a model of three partial differential equations

The propagation and collision behavior of $$\varvec{\delta }'$$ waves in a model of three partial differential equations

Simulation of collision behaviour between droplet and solid surface in liquid phase environment

AbstractProcesses involving dispersed immiscible fluids occur across the traditional onshore and offshore crude oil development phases, including oil exploitation and production, gathering and transportation, and station and field processing. The stabilities of such processes are deeply influenced by the collision and film drainage between separated phase interfaces. Due to factors such as gravity as well as buoyancy and resistance, droplets usually collide with the wall at a relatively high speed and experience one or several rebounds before gradually stabilizing and staying on the surface. Though work related to this aspect has raised significant attention, further research on the force‐deformation behaviour between microsized (r ≈50 μm) droplets and solid surface under the influence of the above factors is still lacking and strongly demanded. In this paper, under the comprehensive influence of flow driving, an emulsified water droplet colliding with a solid surface in silicon oil is modelled. The dynamic behaviour of the droplet was analyzed by coupling the Stokes–Reynolds drainage equation, the generalized Young–Laplace equation, and the force situation of the deformable droplet. Furthermore, the effects of interfacial tension, collision velocity, and viscosity of continuous phase on the collision characteristics of droplet were analyzed, and it was found that these factors could significantly change the collision characteristics of droplet.

Modeling, driving characterization of collision and stick-slip vibration-driven system

Abstract Considering the internal collision vibration-driven and external discontinuous resistance tolerance fusion conditions, the non-smooth dynamics characteristics of collision and stick-slip vibration-driven system are studied and experimented. Unilateral collision behavior of internal oscillators under the action of a periodic force to achieve system motion in different directions, it overcome the external Coulomb friction force and drives the system to drive in steady state under a certain direction. The kinematic and dynamic models of the system are established, and the collision and stick-slip driving motion of the system is analyzed based on the theory of non-smooth dynamics. The voice coil motor is used as the internal driving element, and the vibration driving test platform is designed and fabricated, and the driving characteristics of the system are studied experimentally. The study shows that there are three forms of movement in the steady state driving motion of the system: sticking motion, forward motion and backward motion; sine wave excitation and triangular wave excitation as input excitation have the characteristic of smoother operation with less shock; external excitation parameter regulation can change the system speed and direction of the movement; excitation frequency as a regulation parameter has the advantages of speed bandwidth, continuity, and so on; the system average driving speed in the numerical simulation and experimental test with the system average driving speed in numerical simulation and experimental test has the same rule of change, the backward motion is located in the low-frequency region, the forward motion is located in the high-frequency region, the friction coefficient and the excitation amplitude affect the size of driving speed. The results and methods of this study provide a corresponding theoretical basis for the design and parameter optimization of vibration-driven robots.

Enhancing damping-like efficiency by low-energy mixed ions bombardment

Pursuing enhanced spin–orbit torque (SOT) has become a significant focus for achieving energy-efficient spintronics devices. Researchers have explored different materials, layer engineering, and various post-deposition modification methods to realize higher SOT. Here, we have utilized the bombardment of mixed ions (Ar+ and He+ in various ratios) with 0.6 kV bias voltage to enhance the SOT efficiency in a Pt/Co/W stack. The bombardment modifies the physical properties (magnetic, electric, and structural) due to cascade collision, knocking off atoms (from the surface), and ion implantation. The increased percentage of He+ suppresses the drastic behavior of cascade collisions, and hence, the properties are tunable by changing the gas ratio. We exploited this behavior to design a material stack with enhanced SOT efficiency. We fabricated Hall bars to quantify SOT and observed a 4.5× increase in the effective damping-like efficiency. The efficiency and switching current density in the stack could be tuned by the variation of Ar:He ion ratio and the exposure duration. This study offers an easy route to tune the energy efficiency of spin devices, contributing to the advancement of next-generation spintronics.

The collision behaviors of non-spherical regular particle-wall in three-dimensional space: Experimental investigation

The edges and corners of non-spherical particles cause random bounces in three-dimensional space after the particle-wall collision. To study the collision behaviors, four kinds of non-spherical regular particles are prepared, and the collision test system with a dual-camera is built. The collision process is characterized by introducing the lateral velocity and lateral angle. The rebound angle, lateral angle, and recovery coefficients under different particle diameters and impact angles are obtained. The results show that the rebound angle, lateral angle, and recovery coefficients of non-spherical regular particles are highly dispersed. The mean rebound angles of non-spherical regular particles are significantly smaller than that of spherical particles. The particle diameter, impact angle, and recovery coefficients are in negative correlation. The normal recovery coefficients of non-spherical particles are greatly reduced, and the tangential recovery coefficients change slightly. The recovery coefficients can be applied to multi-phase flow simulations to improve the simulation accuracy.

New theoretical developments on the early-time dynamics and approach to equilibrium in Heavy-Ion collisions

We discuss recent theoretical developments in understanding the early pre-equilibrium dynamics and onset of hydrodynamic behavior in high-energy heavy-ion collisions. We highlight possible experimental signatures of the pre-equilibrium phase, and present recent progress in developing a consistent theoretical description of collective flow in small systems.

Comparing two cryptographic hash algorithms: SHA-512 and whirlpool- a case study on file integrity monitoring

SHA-512 and Whirlpool are two distinct hashing algorithms in the cryptography domain. Although they are different, these methods share some characteristics; such as both of them produce secure digests of the same size. In addition, being increasingly used for sustaining the integrity of confidential files. As a result, it is crucial to explore a method to contrast and compare their performance. This paper presents a comparative analysis of SHA-512 and Whirlpool, in terms of: time consumption, avalanche effect, and resistance to collision. It also investigates their suitability in the context of File Integrity Monitoring. Our results reveal that Whirlpool outperforms SHA-512 in the avalanche effect scenario, whereas a comparable resistance to the collision behavior is exhibited. Regarding time consumption, it is slower than SHA-512. However, this positively reflects its resistance to brute force attacks.

Surface Enhanced Raman Spectroscopy Studies on the “Hot Spot” Localized Area from Free Collision Behavior of Gold Nanoparticle-Gold Single Crystal Microplate

Surface Enhanced Raman Spectroscopy Studies on the “Hot Spot” Localized Area from Free Collision Behavior of Gold Nanoparticle-Gold Single Crystal Microplate

Small-scale computational fluid dynamics modelling of the wave induced ice floe-grease ice interaction in the Antarctic marginal ice zone

Computational sea ice models have been developed to simulate sea ice formation, melt and motion characteristics on a regional scale. However, the highly dynamic sea ice behaviour in the Antarctic marginal ice zone (MIZ), the area where sea ice and ocean waves interact, still eludes reliable prediction. This is due to the complex sea ice composition consisting of relatively small and mobile ice floes governed by collision and fracture mechanisms. To improve the accuracy of sea ice models, the realistic sea ice distribution needs to be accounted for at a high resolution so that key aspects defining the interplay of ice motion and wave propagation can be suitably distinguished. In this work a computational fluid dynamics model based on the small-scale continuum approach has been developed to simulate the dynamics of a heterogeneous sea ice cover. The model makes use of a realistic sea ice layout and studies the mechanical behaviour of sea ice as affected by wave forcing and the specific material properties of ice floes and grease ice. Taking advantage of the continuum approach paired with a heterogeneous sea ice cover, the floe-grease ice interaction is elucidated by discussing detailed temporal and spatial distributions of the mechanical response of sea ice. Results show that the interplay between waves and the ice floe collision behaviour is directly controlled by sea ice inertia, where the frequency and severity of ice floe collisions increase with the wave period. Furthermore, the interaction of grease ice with ice floes through form drag at the interface leads to high localised grease ice strain rate gradients and low viscosity values due its shear thinning characteristics.

An interface-enhanced discrete element model (I-DEM) of bio-inspired flexible protective structures

Natural organisms have evolved protective structures that help them survive environmental threats without sacrificing flexibility. While the discrete element method (DEM) has been used to model bio-inspired flexible protective structures, existing DEM models struggle with modeling interactions between elements of complex geometries and finite deformation, making them unsuitable for describing interfacial interlocking and associated failure mechanisms observed in experiments. Here, we propose an interface-enhanced DEM (I-DEM) model that brings about a number of advantages over the existing methods. First, contact-induced geometric nonlinearity is incorporated via a nonlinear interaction function to model interfacial interlocking. Second, finite deformation of interfacial material is taken into account in modeling interfacial failure. Furthermore, contact detection and processing algorithms are utilized to model collision and post-contact behaviors. The utility of I-DEM is demonstrated in modeling bio-inspired flexible protective structures across three distinct interfaces, evidencing its broad applicability to varied interface geometries. FEM simulations of scaled armor structures with segmented helmet and space shield are performed to demonstrate an increase in computational efficiency of the proposed I-DEM model by about four orders of magnitude for static analysis and by two orders of magnitude for dynamic analysis, with numerical discrepancies within about 10%, compared to FEM.

Analysis of dynamic interaction and response in multispan girder bridges subjected to near-fault earthquakes

This study delves into the separation and collision behavior of multi-span bridges with plate rubber bearings, focusing on the influence of seismic excitation period and vertical/horizontal acceleration (V/H) ratio during near-fault earthquakes. Employing the modal superposition approach, a four-span bridge model is scrutinized to understand the dynamic interaction between its components under seismic forces. The main girder, supports, and piers are simplified into beam, spring, and rod elements, respectively, to analyze vertical movements and collisions. Different bridge positions are evaluated for separation using the transient wave function, and the vertical impact force during collisions is assessed via the indirect modal method. It emerges that bridge separation is likely when excitation periods align with the bridge's natural frequency, especially for multi-span structures. These bridges also demonstrate a 25–110% increase in vertical collision forces compared to double-span bridges under various excitation periods, surpassing V/H= 2/3 standard. Theoretical energy-based calculations corroborate these observations.

Dynamic collision estimator for collaborative robots: A dynamic Bayesian network with Markov model for highly reliable collision detection

In this paper, we propose a highly reliable and accurate collision estimator for robot manipulators working in human–robot collaborative environments, based on the Bayesian approach for practical uses. We assume the robot collision as a dynamic Markov process, not a static event, to reflect the transient behavior of mechanical collisions. Thus, the collision estimator can integrate the prior belief on collision and the measurements on the robot state, to produce the current belief on the robot collision in a usual recursive form. An exponential form of observation model, serving as the likelihood function, is constructed on the projected observation domain by using the multi-variate statistical information of empirical models of collision and non-collision cases. The proposed method is validated by using a commercial 7 degree-of-freedom (DOF) collaborative robot arm with random impacts along the links while it is in motion. Results show that the proposed collision estimator achieves a compelling performance with collision estimation time of 8.86ms on average, an overall accuracy of 99.47%, and zero occurrence of false alarm.

Experimental study of particle collision and rebound with moving walls

Particle–wall collision always occurs in transportation systems with multi-phase flows containing particles in pneumatic conveying, coal liquefaction production, and wastewater treatment. Especially within rotating fluid machinery, collision and rebound between particles and moving walls occur frequently. It is necessary to conduct research, as it can provide theoretical support for controlling particle trajectories and reducing particle erosion. In this study, experimental investigations are carried out to analyze the trajectories and restitution coefficients of particle collision and rebound at different velocities of the moving wall, wall roughnesses, and collision angles. Particle trajectories and the influence of particle rotation on restitution coefficients in normal collisions are investigated, and particle motion behavior, tangential and normal restitution coefficients of the particle collision and rebound, and effective rebound angles in oblique collisions are analyzed and discussed at different operating conditions. The differences in collision and rebound characteristics between normal and oblique particle impacts are identified.

Numerical investigation on heat transfer and vapour layer geometry of a droplet impacting on a spherical particle in Leidenfrost regime

Understanding the heat transfer mechanism and dynamic behaviors of droplet-particle collision in Leidenfrost regime is essential for the pyrohydrolysis process of pickling liquor, which is sprayed into a fluidized bed and then decomposes to oxides and acid vapour. In this study, the droplet deformation, heat transfer characteristics and vapour layer geometry of Leidenfrost droplet impacting spherical particle are investigated by constructing a microscale phase change model in VOF framework. The applicability of the computational model in capturing droplet dynamics and thermodynamics is verified by comparing it with experimental outcomes. The results indicate that the vapour layer geometry is relatively uniform in spreading but shows instability in recoiling. The vapour layer thickness increases rapidly in both spreading and early recoiling, while decreases in the late recoiling phase. Furthermore, the heat transfer and droplet evaporation depend on the vapour layer thickness strongly. Specifically, the thinner the vapour layer, the lower the heat transfer resistance. The increasing surface temperature, We and Re can effectively enhance heat transfer and raise droplet temperature. In addition, the maximum spreading factor and liquid–solid contact time play an important role in heat transfer and they both show a clear power-law dependency on We and Re for viscous droplets. The effect of droplet size on contact time is consistent with first-order vibration theory but the contact time is independent of surface temperature and impact velocity.

A finite‐discrete element model for simulating collision and fragmentation of nanoparticle agglomerates

AbstractThe fragmentation/adhesion behavior of nanoparticle agglomerate collision, which is challenging to model, is a crucial factor affecting fluidization. In this study, a discrete‐finite element method (FDEM) based cohesive crack model is developed to simulate normal collisions between a complex agglomerate (around 1 mm) and a wall. In the FDEM model, the complex agglomerate is built from primary agglomerates (around a few micrometers), whose adhesive force and Young's modulus are measured by an atomic force microscope (AFM). The simulation results including fragmentation morphology and plastic deformation agree well with the collision experiments. Finally, the sensitivity of the model is tested, including adhesive force, solid holdup, and Young's modulus. Fragment distribution is found to fit well with a two‐parameter Weibull function and damage ratio is found to have a polynomial relation with a modified Weber number. The model output shows a potential to be utilized in macroscopic model.

Particle motion analysis of a new three-phase fluidized bed flotation column with glass sphere particles

Analysis of the particle movement within the unit vessel is necessary for the design, optimization and scale-up of the new three-phase fluidized bed flotation column (TFC). This work aimed to examine the motion and distribution of assisted fluidized particle-glass spheres in the TFC and to provide a better assessment of particle collision and dispersion behavior by quantifying particle velocities. Tracer particles were analyzed by high-speed camera techniques to determine particle velocity fluctuations in a three-phase fluidized bed consisting of glass spheres, water, and bubbles. A correlation model for determining the particle velocity in a three-phase fluidized bed is proposed after a systematic analysis of the particle velocity. The model covers a wide range of superficial gas velocities (0–0.339 m/s), superficial liquid velocities (0.169–0.425 m/s) and initial static bed heights (0.162–0.262 m). Aiming to evaluate particle collisions in the TFC, this paper derives the particle collision frequencies using a modified collision model and investigates the effect of a wide range of operating parameters on particle collisions. Finally, a new method for estimating dispersion due to particle motion is developed based on the study of particle dispersion coefficients.

Electrochemical and electroluminescent behaviors of single meldola’s blue-ruthenium (II) bipyridine composite nanoparticles colliding onto an ultramicroelectrode

Stochastic collision nanoelectrochemistry (SCNEC) of single nanoparticles (NPs) is an emerging electrochemical method with significant potential. Herein, we synthesized a new kind of NPs, named Meldola’s Blue-ruthenium(II) bipyridine (MDB-Ru) for the first time with the help of ultrasonic energy, and investigated the properties of the single NPs by SCNEC. The quantitative relationship between the concentration of MDB-Ru NPs and the collision frequency was obtained by optimizing collision experimental conditions. By comparing the theoretical calculation with the experimental value, it is speculated that signal loss may be caused by the aggregation of NPs or the large background currents. Furthermore, the electrochemiluminescence (ECL) performance of MDB-Ru NPs colliding in the presence of different co-reactants (TPrA/DBAE) was thoroughly discussed. The results demonstrated that the MDB-Ru NPs can produce a higher current response, and with respect to TPrA, using DBAE generated a higher ECL intensity (∼2 times). Moreover, electrochemical and ECL were employed to simultaneously investigate the collision behavior of MDB-NPs, in which demonstrated a strong correlation between the two techniques. This research has broad implications for studying fundamental aspects of SCNEC in organic dyes and provides a foundation for developing analytical sensor techniques using single entity electrochemistry and ECL.

Effect of cell settlement on the electrochemical collision behaviors of single microbes

Electrochemical collision technique has emerged as a powerful approach to detect the intrinsic properties of single entities. The diffusion model, together with migration and convection processes are generally used to describe the transport and collision processes of single entities. However, things become more complicated concerning microbes because of their relatively large size, inherent motility and biological activities. In this work, the electrochemical collision behaviors of four different microorganisms: Escherichia coli (Gram-negative bacteria), Staphylococcus aureus, Bacillus subtilis (Gram-positive bacteria) and Saccharomyces cerevisiae (fungus) were systematically detected and compared using a blocking strategy. By using K4Fe(CN)6 as redox probe, the downwards step-like signals were recorded in the collision process of all the three bacteria, whereas the collision of S. cerevisiae was rarely detected. To further investigate the underlying reason for the abnormal collision behavior of S. cerevisiae, the effect of cell settlement was discussed. The results indicated that ellipsoidal S. cerevisiae with a cell size larger than 2 μm exhibited a cell sedimentation rate of 261.759 nm s−1, which is dozens of times higher than the other three bacteria. By further enhanced convection near the microelectrode or positioned the microelectrode at the bottom of electrochemical cell, the collision signals of S. cerevisiae were successfully detected, indicating cell sedimentation is a nonnegligible force in large cell transport. This study fully addressed the effect of cell settlement on the transport of microbial cells and provided two strategies to counteract this effect, which benefit for the deeper understanding and further application of electrochemical collision technique in single-cell detection.

Effect of energy input on flotation of particles with different sizes: Perspective of hydrodynamics characteristics

By employing a torque sensor to measure energy input in a flotation machine, this paper investigates the flotation behavior of modified quartz particles with different sizes but similar surface hydrophobicity under various energy input conditions. Numerical simulations of the mechanical flotation machine were conducted to obtain the fluid dynamic characteristics including the flow velocity, turbulence kinetic energy, and turbulent eddy scale. With the flotation results and numerical simulations combined, the potential collision, attachment, and detachment behaviors of fine particles (―45 µm), intermediate particles (45―74 µm), and coarse particles (74―125 µm) were analyzed. The results demonstrate that under different conditions of energy input, the recovery of intermediate-sized particles was optimal for the above size fractions. As the particle size increases, the energy input required to achieve optimal recovery decreases. The flotation rate constants increase nearly linearly with energy input. Compared to the medium-sized particles in the range of 45―74 µm, finer and larger particles exhibit lower floatability. When the energy input exceeds a certain range, no stagnation zone is observed. The rupture of bubble-particle aggregates becomes more pronounced, which may be a reason why flotation recovery begins to decrease. Increasing energy input enhances turbulence energy dissipation and reduces the Kolmogorov turbulence length scale, in this study, the ―45 µm, 45―74 µm, and 74―125 µm particle sizes reached the optimal flotation performance at dp / η values of 1.35, 1.83, 2.54, respectively. The particle diameter-to-integral length scale ratio (dp/L) is also discussed as an important parameter for turbulent dispersion.